Efficient Beacon Transmission and Reception

ABSTRACT

A control point, such as a laptop, phone, wireless access point, or other device, transmits beacons to receiving stations in a wireless network. The control point may reduce power and bandwidth consumption by transmitting beacons with smaller payloads and/or less frequently to sectors with no associated stations. The stations, which may include laptops, phones, or other devices may reduce power consumption be powering on their antennas when beacons may be transmitted to their sectors.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Application Ser.No. 61/890,520, filed Oct. 14, 2013, which is incorporated herein byreference in its entirety.

BACKGROUND

1. Technical Field

This disclosure relates to beaconing in wireless communicationprotocols.

2. Related Art

Today, a spectrum of electronic devices that incorporate wirelesscommunication technologies is available. For example, cell phones,tablets, global positioning system (GPS) devices, and laptop computersare in wide use. Further, wireless protocols deliver an increasing rangeof service. For example, streaming music and High Definition (HD) videohave seen increased adoption. Demand for such electronic devices may bedriven by their ability to provide the bandwidth used in the delivery ofthese services. Devices that efficiently use wireless spectrum toprovide high throughput may experience increased demand.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example wireless communications environment.

FIG. 2 shows an example beacon transmission interval.

FIG. 3 shows an example pseudo-randomized directional beacontransmission process.

FIG. 4 shows an example network with a control point (CP) and multiplenon-CP stations (STAs).

FIG. 5 shows an example transmit sector sweep.

FIG. 6 shows an example CP transmitting directional beacons acrossmultiple sectors.

FIG. 7 shows example logic for sector determination during the beacontransmission interval (BTI).

FIG. 8 shows example logic for non-CP STA reception of beacons duringthe BTI.

FIG. 9 shows example logic for transmission of beacons.

FIG. 10 shows example timing diagrams for beacon transmission.

FIG. 11 shows an example beacon transmission environment.

FIG. 12 shows an example transmit antenna sector identification patterninformation element.

FIG. 13 shows example logic for reception of beacons.

FIG. 14 shows example logic for reception of beacons.

FIG. 15 shows example logic for receive sector updates.

FIG. 16 shows an example timing diagram for beacon intervals.

FIG. 17 shows example logic for beacon transmission.

FIG. 18 shows an example beacon transmission environment.

DETAILED DESCRIPTION

The disclosure below concerns techniques for efficient beacontransmission and reception. A wide variety of different wirelesselectronic devices may implement these techniques. Accordingly, thewireless communication environment example described below provides anexample context for explaining the beaconing techniques. In other words,the environment is just one example of a wide array of environments anddevices that may incorporate the beaconing techniques.

FIG. 1 shows an example wireless communications environment 100. In oneexample, multiple devices 101, 151 may communicate over a wirelessprotocol. The devices may be virtually any wireless enabled device. Forexample, laptops, tablets, cellular telephones, access points, networkcontrollers, audio/visual equipment, data storage device, portablegaming systems, and/or other wireless enabled devices.

The station (STA) 101 may include one or more processors 104 to supportexecution of applications and general operation of the STA. The STA 101may include memory 106 for execution support and storage of systeminstructions 108 and operation parameters 112. The STA 101 may alsoinclude one or more wireless interfaces 114 to support over-the-aircommunications. The wireless interfaces 114 may be operatively connectedto a directional antenna 113. The wireless interfaces may includebaseband processors, signal processing hardware, and other signalcomponents to support communications by the STA 101 over one or morewireless protocols. The wireless interfaces may support protocols suchas wireless local area network (WLAN) (IEEE 802.11ad and or other WLANprotocols), cellular data/voice (LTE/LTE-A, 4G, 3G/2G, and/or othercellular protocols), Bluetooth, WiMAX, or other wireless protocols. Thedirectional antenna may include multiple antennas for varied protocols.Multiple antennas of the directional antenna may be used for directedtransmission/reception and/or transmitting/receiving signals withvarying spatial modes. In various implementations, directedtransmission/reception may be achieved via phased-array beam steering.In some implementations, various functions of the directional antenna113 may be performed by a single antenna, which may be directed oromnidirectional. The STA 101 may include a user interface 116 to allowfor user operation of the STA.

The STA 101 may be in communication with a second STA 151 via the STAs'wireless interfaces 114 and 164, respectively. The STA 151 may alsoinclude one or more processors 154 and memory 156 for execution supportand storage of system instructions 158 and operation parameters 162. TheSTA 151 may also include a directional antenna 163, which may includeone or more antennas.

The STAs 101, 151 may communicate over a common wireless protocol 199which may be dependent on beaconing for communication link maintenance.In various implementations, the STAs 101, 151 may communicate in an adhoc network arrangement. Alternatively or additionally, one of the STAsmay act as a coordination device or control point (CP) for a group ofSTAs (including STAs 101, 151) in an ad hoc arrangement. In some casesone of STAs 101 and 151 may act as an infrastructure element, such as anaccess point, router, network controller, or other infrastructureelement. Additionally or alternatively, STAs 101 and 151 may communicatevia a third STA acting as an infrastructure element.

In some cases, wireless protocol 199 may be a high throughput. Forexample, the 802.11ad standard may offer throughput of up to 7 Gbps ormore in wireless data transmissions.

In some implementations, the wireless protocol 199 may be a networkusing a personal basic service set (PBSS). For example, an IEEE 802.11adnetwork. In some cases, the STAs in the network may communicate directlywith one another. In some PBSS networks one STA assumes may the role ofthe CP. The CP may provide the basic timing a PBSS network through abeacon frame. Allocation of service periods and contention-based accessperiods may also occur in the beacon frame. Additionally oralternatively, some of the functionality of the beacon frame may beaccomplished in an announce frame.

In some cases, to act as a CP a STA may include determinedfunctionalities. For example, a CP may have directional multi-gigabit(DMG) communication capabilities.

In some implementations, multiple STAs within a PBSS network may becapable of operating as a CP. The role of CP may be passed among STAscapable of operation as a CP. The CP services (CPS) may be provided bythe STA which is currently acting as the CP. In some implementations,Non-CP STAs may not provide CPS. CPS may include services such as,beacons, association instructions, disassociation instructions,reassociation instructions, quality of service (QoS) traffic scheduling,and/or other services.

Timing in the wireless protocol 199 may be divided into beaconintervals. FIG. 2 shows an example beacon transmission interval 200. Thebeacon interval may be subdivided into a beacon header interval (BHI)202 and a data transmission interval (DTI) 210. Beaconing and networkmanagement tasks may be performed during the BHI. Data payload transferand management tasks may be performed during the DTI. Additionally oralternatively, data payload transfers may occur during the BHI. The BHI202 and DTI 210 may be divided into access periods. Different accessperiods within an interval may have different access rules. Theparameters of the access periods may be detailed in a schedule that iscommunicated by beacons from the CP to the non-CP STAs within thenetwork. In various implementations, the BHI may be divided into accessperiods including the BTI 204, the association beam forming trainingaccess period (A-BFT) 206, the announcement transmission interval (ATI)208 and/or other access periods. The DTI may be divided into accessperiods including contention based access periods (CBAPs) 212, 218,scheduled service periods (SPs) 214, 216, and/or other access periods.

During the BTI 204, beacon frames, such as DMG beacon frames, may betransmitted. Beacon frames may be detectable by non-CP STAs. In somecases, beacon frames may include low bit-rate data. For example, lowbit-rate data may be supported by legacy STAs and/or STAs that do notsupport multi-gigabit data. In some cases, non-CP STAs in the networkmay not transmit during the BTI 204.

During the A-BFT 206 beamforming training may be performed. In somecases, training may be performed with the CP which transmitted beaconsduring the BTI. In various implementations non-CP STAs may performbeamforming training directly with other non-CP STAs. In some cases, theCP may determine to include or not to include the A-BFT in the BHI. TheCP may signal the presence of the A-BFT in beacons during the BTI.Additionally or alternatively, the timing of the A-BFT may be defined inthe beacons transmitted during the BTI. In various implementations, theCP may determine to include or to not include individual STAs forparticipation in the A-BFT. Participation may be signaled in the BTI.

During the ATI 208, the CP may engage in a request-response basedmanagement access period between CP and non-CP STAs. In some cases, theCP may determine to include or not to include the A-BFT in the BHI. TheCP may signal the presence of the ATI in beacons during the BTI.Additionally or alternatively, the timing of the ATI may be defined inthe beacons transmitted during the BTI. In various implementations, theCP may determine to include or to not include individual STAs forparticipation in the ATI. Participation may be signaled in the BTI.

The DTI may include a number of CBAPs. In the example DTI 210, two CBAPs212, 218 are included. During a CBAP, STAs may gain access to thecommunication medium, e.g. spectrum at 60 GHz, 2.4 GHz, a directedcommunication path or other medium via a contention based access scheme.In a contention based access scheme, access to transmission resourcesmay be unscheduled. For example, a STA with an impending transmissionmay request other STAs to be silent during for a period. The period maybe requested by the STA, or may be determined by other factors. Forexample, the length of the silence by the other STA may be dependent onthe quantity of data the transmitting STA sends, the time that thetransmitting STA uses the transmission medium, requests made by otherSTSs to transmit, a maximum time/data amount that may be reserved with arequest, and/or factors.

During the SPs 214, 216, the CP may schedule access to the communicationmedium for the non-CP STSs. For example, the STSs may make requests fortransmission resources, such as a transmission window on a directedcommunication pathway, from the CP. The CP may provide a resource grantin response.

In some implementations, a STA, such as an STA with DMG functionality,may access a communications channel during a beacon interval. The accessmay be CP-coordinated using a schedule. The CP may generate the scheduleand communicate the schedule to STSs during the BTI and/or ATI. Non-CPSTSs that receive the scheduling information may access the mediumduring the scheduled periods using the access rules defined in theschedule.

In various implementations, the CP may control the timing within thenetwork. In some cases, timing indicators in the form of timingsynchronization function (TSF) for timing synchronization may beprovided by the CP, e.g. in a PBSS network. The CP may transmit abeacon, e.g. a DMG beacon, that contains a TSF timer value. Other STSsin the network may synchronize their TSF times to the CP timer valuefrom the beacon. In various implementations the CP may transmit thebeacon during the BTI. A receiving non-CP STA may accept the timinginformation from an associated CP. In some cases a non-CP STA may have atimer value for the TSF that does not match the timestamp a beaconreceived from the CP. The non-CP STA may change its own timer value tomatch the timestamp received in the beacon from the CP.

Additionally or alternatively, the beacon transmitted by the CP mayinclude other parameters for the wireless protocol 199. The beacon maycontain one or more information elements (IEs) that may be used by a STAto join the wireless network controlled by the CP. For example, a DMG CPCapability IE may be included and may be used by new STA during anetwork join operation. Additionally or alternatively, the beacon mayinclude other IEs, such as, DMG STA Capability IEs for advertisinginformation about associated STAs in the wireless network, ExtendedSchedule IEs to schedule traffic streams, Wakeup Schedule IEs toschedule power saving processes, Awake Window IEs to scheduleannouncement traffic indication message (ATIM) frames, STA AvailabilityIEs which may contain lists of STAs in the network which may beavailable in the subsequent access periods, and/or other IEs.

The CP may transmit beacons for different configuration of itsdirectional antenna. For example, DMG beacon transmission may beperformed using multiple directional transmissions, and a beacon may besent in different ones of the directions. A CP may change the sequenceof directions through which beacons are transmitted. For example, afterthe CP has transmitted a DMG beacon frame through the directions in thecurrent sequence of directions, the CP may implement a new sequence fora subsequent round of beacon transmissions. In various implementationsthe CP may implement random, pseudo-random, and/or deterministic DMGbeacon transmission sequence changes. In some cases, the randomsequencing of the DMG beacon may randomize interference to/from thebeaconing process. FIG. 3 shows an example pseudo-randomized directionalbeacon transmission process 300. During the BTIs 322, 324, 326, 328within the beacon intervals 302, 304, 306, 308, the directional beaconsare transmitted in a sequence 342, 344, 346, 348. In the example of FIG.3, the sequences 342, 344, 346, 348 may be pseudo-randomly selected froma listing of possible sequences for the transmitting CP.

In some cases, a STA acting as a CP may be a battery powered portabledevice, for example, laptop, mobile phone, PDA device, or other portabledevice. Reducing the power consumption of the CP may contribute toincreased commercial success of the CP device.

FIG. 4 shows an example network with a CP 402 and multiple non-CP STAs404, 406. In the example, the CP 402 may be a laptop computer. Thenon-CP STAs 404, 406 may be a video monitor and a cellular phone. Thenon-CP STAs may engage in directional communications directly. In somecases, the CP 402 may coordinate the wireless protocol among the STAs,and the STAs may not use the CP as an intermediary in directcommunications. In some implementations, the CP may act as anintermediary for STAs engaged in indirect communications.

In some cases, it may be advantageous to maximize transmission resourcesused for data transmission and to minimize resources used in networkmanagement while maintaining network robustness and reliability. Beacontransmission may be a regular and/or frequent activity for a CP e.g.recurring with beacon intervals. It may be advantageous to minimize theresources used in beacon transmission to reduce power consumption by theCP and to increase resources available for data transmission.

In some implementations, a beacon may be used as a beamforming (BF)training frame. For example, in the IEEE 802.11ad standard, a DMG beaconmay be used in the BF training process. The BF process may begin with asector level sweep (SLS) from the initiator. A directional beacontransmission may be used as an SLS where the CP is the initiator. Non-CPSTAs may perform SLSs outside of the CP beacon process. Non-CP STA SLSsmay enable direct communications between STAs that do not use the CP asan intermediary. A beam refinement protocol (BRP) may follow the SLS,for example, if requested by either the initiator or the responder. TheSLS phase may enable communications between the two participating STAsat the control PHY rate or via a high throughput modulation and codingscheme (MCS). The control PHY rate may be associated with lowthroughput. The control PHY rate may be supported by the devices in thenetwork. For example, legacy or low capability devices may support thecontrol PHY rate and not support one or more high throughput MCSs. Insome implementations, the SLS phase provides transmit BF training. TheBRP phase may enable receiver training and iterative refinement of theantenna weight vectors (AWV) of the transmitters and receivers of theparticipating STAs. In some cases, the total number of sectors for adirectional antenna may range from 1 to 128 sectors. In someimplementations the number of sectors may vary over an extended range.

A directional antenna may include a phased array, a single elementantenna, a set of switched beam antennas covered by aquasi-omnidirectional antenna pattern, or other directional antennastructure. A transmit sector sweep (TXSS) may be performed during beacontransmission. A TXSS may rotate beacon transmission through antennasectors in pseudo-random order in BTI during one or multiple beaconintervals. Additionally or alternatively, a random rotation throughbeacon transmission sectors may be used. In some implementations, TheTXSS can contain 128 sectors per directional antenna. In some cases, 16or 32 sectors may be used. FIG. 5 shows an example transmit sector sweep500. The beacon transmissions 502 occur in a pseudo-randomly selectedorder.

Non-CP STSs, either joining the network or already associated, mayoperate their directional antennas in an omnidirectional orquasi-omnidirectional mode during reception of directional beacons. Theinitiator and/or CP transmitting the directional beacons may report thedirection associated with the beacon within the content of the beacon.The responder receiving the beacon may be able to determine thedirection of the beacon from the report. FIG. 6 shows an example CP 602transmitting directional beacons 612 across multiple sectors. The STA604 may receive one or more of the beacons while operating its antennain a quasi-omnidirectional receive pattern 614. For example, the STA 604may operate a DMG antenna in a mode with a wide beamwidth, i.e. a modewith large solid angle coverage.

The airtime used in transmission of a beacon may increase with thebeacon payload size. If the number of STSs in a network increases, thenumber of IEs in the beacon frame may increase, and the airtime used mayincrease. The beacons may be transmitted at the control PHY. The lowthroughput of the control PHY may be associated with large airtimeincreases for increases in beacon payload content. CP beacontransmission may recur at the beacon interval. The time used by BTIs maybe a large portion of the total airtime. This may increase the powerconsumed by the CP while transmitting beacons. Additionally oralternatively, the time used by the BTIs may reduce the time availablefor data transmission. For example, the time in the beacon intervalreserved for the SP, CBAP, or other data access period may be shortenedto allow for the increased time usage by the BTI.

FIG. 7 shows example logic 700 for sector determination during the BT.The CP may generate a pseudo-random transmit sector ID (702). The CP mayprogram its AWV for the sector associated with the sector ID (704). TheCP may then transmit a directional beacon in that sector (706). The CPmay repeat sector ID generation 702, AWV programming 704, transmission706 for the antenna sectors (708). The CP may repeat, at the beaconinterval, transmission of the directional beacon frames in the pseudorandomly selected sectors.

FIG. 8 shows example logic 800 for non-CP STA reception of beaconsduring the BTI. During the BTI, the non-CP STAs, may configure theirantennas in quasi-omnidirectional mode and receive the directionalbeacons (802). The non-CP STAs may listen for the duration of the BTI toavoid missing a pseudo-randomly ordered beacon (804). The non-CP STAsmay turn on their receiver and power their antennas for the duration ofthe BTI. The non-CP STAs may repeat quasi-omnidirectional modeconfiguration 802 and listening 804 with the beacon interval. Poweringthe receiver and antennas for the duration of the BTI may be associatedwith increased power consumption.

In some cases, the CP may optimize the beacon transmission time, whichlead to power savings and increased available bandwidth for payload datatransmission.

In some implementations, the STAs may reduce the duration in which theyturn on their receiver and maintain their quasi-omnidirectional antennain a powered mode. This may lead to power savings.

In some implementations, the CP may rotate through antenna sector IDs inN beacon transmissions, where N is the number of antenna sectors. Thisrotation may provide good spatial coverage and low latency. UnassociatedSTAs may receive beacons while in previously unused sectors and join thenetwork.

In some cases, BF may be initiated between two devices, e.g. a STA and aCP, before any data communication occurs. BF may include TXSS and a BRP.TXSS may enable the BF STAs to discover each other and to determineinitial transmitter AWV settings. A STA receiving a TXSS from anotherSTA may reply to the TXSS with a selected sector for the receiving STA,e.g. the sector with the highest signal-to-noise ratio (SNR), or asector with a high SNR near other sectors with high SNRs. This may leadto robustness during mobility The BRP may occur after the TXSS for theBF STAs. During the BRP the BF STAs may reconfigure their directionalantennas from a quasi-omnidirectional mode to a determined AWV. Oncedirectional determinations are made, the BF STAs may refine theirdetermined transmit and receive AWV to optimize their respective SNRs.

In some implementations, the CP may send the parameters of the randomSector ID pattern to enable the STAs to predict the pseudo random beaconrotation of the CP. The CP may transmit Antenna Sector ID pattern (TAID)IE to non-CP STAs during management frame exchanges, e.g. during theBTI, A-BFT, and/or ATI.

The inclusion of IEs such as, extended schedule IEs, awake window IEs,DMG STA capability IEs, wake up schedule IEs, and/or other IEs mayincrease the size of the BTI. Such IEs may not be used by unassociatedSTAs. In some cases, information such as the TSFs, SLSs, beacon intervalcontrols, and/or DMG parameters may be used by STAs attempting to jointhe network. It may be advantageous to include IEs used by STAsattempting to join the network in beacon transmissions to sectors withassociated STAs and sectors without associated STAs. Forassociated-station IEs not used by STAs attempting to join the network,i.e. unassociated STAs, it may be advantageous to transmit theseassociated-station IEs to sectors with associated STAs and forgotransmission to sectors without associated STAs.

In an example implementation, a CP may have a directional antenna with16 sectors. In the example there are no associated STAs in the network,and the CP transmits a beacon length of 70 bytes. In the example, thecontrol PHY rate is about 133 kbytes/s. This corresponds to a BTI of528×16=8448 μs. When a single STA joins the network, the STA CapabilityIE may be added to the beacon content. The beacon length increases by 19bytes, making the BTI 608×16=9728 μs. A 19 byte increase increases theBTI by 1.28 ms. In some cases, the BTI may repeat with the beaconinterval, which may have a 100 ms spacing. The access periods for datatransfer in the beacon interval may be shortened by 1.28 ms to accountfor the increased BTI. The potential data bandwidth may be reduced byabout 1.5% by adding one STA. In the example, the control PHY may beless than the maximum throughput for the network. The 1.28 ms lost tothe data transfer access periods, e.g. SPs and CBAPs, may be greaterthan the 19×16=304 bytes added to the bandwidth of the BTI. In someimplementations, the ratio of bandwidth lost to the DTI and gained bythe BTI may be 7000/1. The ratio may vary with the MCS of associatedwith the access periods.

In some implementations, the CP may transmit beacons with contentsrelevant to already associated STAs in the selected transmit sectors forthose STAs. In the rest of the sectors which are not selected sectorsfor the associated STA, the CP may transmit beacons with IEs used injoining the network. Other IEs may be omitted from the beacon.

FIG. 9 shows example logic 900 for transmission of beacons. The CP mayselect a sector for transmission by generating a pseudo-random sector IDfrom via its sequence generator (902). The CP may compare the generatedsector ID to a listing of selected sectors for associated STA (904). Ifthe comparison indicates that the generated sector ID corresponds to aselected sector, the CP may transmit a beacon with associated-stationIEs for associated STAs (906). Otherwise, the CP may transmit a beaconwith IEs for unassociated STAs (908). The CP may repeat the process forthe sectors of the antenna (910). The associated-station IEs may not betransmitted for the unassociated STAs. Using the logic 900, the CP mayselectively transmit beacons with a smaller payload, reducingtransmission time, in the directions where there are no associatedSTA(s). This may reduce the BTI duration in the beacon intervals.

FIG. 10 shows example timing diagrams 1000, 1050 for beacontransmission. In the example timing diagram 1000 for non-selectivetransmission, the beacon including the associated-station IEs 1060 istransmitted to N sectors (0, 1, 2, . . . , N-2, N-1). In the exampletiming diagram 1050 for selective transmission, sectors 0 and N-2 areselected sectors for associated STAs. Sectors 1, 2, and N-1 are notselected sectors. Beacons 1070 with associated-station IEs omitted aretransmitted by the CP to sectors 1, 2, and N-1. Less time is used inbeacon transmission in the timing diagram 1050 for selectivetransmission.

FIG. 11 shows an example beacon transmission environment 1100. In theexample environment 1100, a CP 1122 is transmitting beacons over 6sectors 1101, 1102, 1103, 1104, 1105, 1106 (sector IDs 0 to 5). The CPhas one associated STA 1123. The STA 1123 is receiving beacons with itsantenna configured in a quasi-omnidirectional receive pattern 1124. CP1122 is transmitting beacons with associated-station IEs for theassociated STA 1123 in sector ID 2 1103. The remaining sectors 1101,1102, 1104, 1105, 1106 receive beacons with the associated-station IEsomitted by the CP 1122 via the logic 900.

In some implementations, the STA may keep its receiver ON for the BTIduration to receive beacons. The STA may listen to beacons for itsselected sector. The STA have its antenna powered during periods inwhich the CP may not be transmitting beacons to the selected sector forthe STA. Since receiving period is repeated in with the beacon interval,the excess power used to listen when the CP may not be transmitting theselected sector for the STA may be cumulative over a number ofrepetitions. If the CP is using selective transmission logic, e.g. logic900, the beacons transmitted to sectors which are not the selectedsector for the STA may not include the associated-station IEs. The STAmay listen for the beacon for its selected sector in case where itreceives a beacon for another sector, e.g. another sector without theassociated-station IEs.

In some cases, the STA may configure its antenna for directionalreception. The STA may use a configuration determined through a previousBF training period with the CP. In some cases, this may bias receptionof beacons to those transmitted to the STA's selected sector.Transmissions to the STA's selected sector may receive increased antennagain when a directional pattern is used. Transmissions to sectors otherthan the selected sector may receive reduced antenna gain.

Additionally or alternatively, the STA may receive a beacon transmissionand determine to which sector the beacon has been transmitted. Forexample, the STA may decode the sector ID from the beacon. If the beaconwas not transmitted to the STA's selected sector, the STA may power downits antenna until the beacon transmission completes. The STA may thenpower up its antenna and receive at least a portion of the next beacon.If the beacon was transmitted to the STA's selected sector, the STA maylisten to the remainder of the beacon.

In some cases, once a STA receives a beacon transmitted to its selectedsector and/or a beacon with associated-station IEs transmitted toanother sector the STA may power off its antenna until the end of theBTI.

In some implementations the non-CP STAs may power up their antennas whenthe CP transmits in their associated selected sectors. The non-CP STAsmay power down their antennas when the CP transmits in other sectors.

During BTI, non-CP STAs may turn ON its receiver to receive the beacontransmitted for its selected sector, using the information provided inthe TAID IE.

In some implementations, a CP may randomly or pseudo-randomly change thesequence by which it sends beacons to sectors in successive BTIs.Changes to the sequence may randomize and potentially minimizeinterference to/from the beacons. In some cases, the sequence ofdirections may be pseudo randomly chosen from a sequence of directionscovering the set of directions available to the CP.

In various implementations, the CP may transmit TAID IE to non-CP STAsduring transmission of a beacon or management frame, e.g. during theBTI, A-BFT, ATI, or other access periods. For example, a managementframe may include an association response containing the TAID IE duringa joining process for a new STA. The STA may determine the sequence ofthe beacon transmission by using the parameters in the TAID IE as inputsto the sector generation algorithm used by CP. FIG. 12 shows an exampleTAID IE 1200. The example TAID IE 1200 includes the length 1202 and type1204 for the sequence to be generated. The example TAID IE 1200 mayfurther include tap 1205, 1206 and/or state 1207, 1208 parameters forgeneration of the sequence. Additionally or alternatively, a TAID IE mayinclude an indicator for the sequence generation algorithm used. In somecases multiple algorithms/sequence listings may be available for use bythe STAs for sequence generation.

For the example TAID IE 1200, the STA may use the received TAID IE 1200to generate the sector ID's for subsequent beacons by advancing thesequence generator initiated using tap 1 1205, and state 1 1207, and thecurrent antenna sector ID. The STA can advance the sequence generator byshifting for each anticipated beacon transmission. According to theproposed method, the STA may advance the sequence generator and evaluatethe sector ID for the upcoming beacon transmission. When the sector IDmatches, the selected receive sector of the STA, the STA may then turnON its receiver. Additionally or alternatively, the STA may turn on itsreceiver during a range to allow for variation in beacon transmissiontimes. For example, a CP using logic 900 may have BTIs of varying lengthas STAs associate or unassociate. The CP may report the number ofassociated STAs in a management frame to aid in predicting thisvariation. The STA may configure its antenna in a directional orquasi-omnidirectional mode.

FIG. 13 shows example logic 1300 for reception of beacons. The STA mayadvance the sequence generator using the TAID IE inputs (1302). The STAmay determine if the current sector matches the STA's selected sector(1304). If not, the STA may skip reception of the beacon and keep itsreceiver and antenna in a powered down mode (1306). If the sector doesmatch, the STA may turn on its receiver and antenna, and receive thebeacon (1308). The STA may configure its antenna with receive beampattern pointing towards the CP using the best receive sector AWV or ina quasi-omnidirectional configuration. The STA may repeat for the lengthof the sequence (1310).

FIG. 14 shows example logic 1400 for reception of beacons. Prior to theBTI or at the beginning of the BTI, the STA may advance the sequencegenerator to the end of the sequence using the TAID IE input (1402). TheSTA may determine the in placing of its selected sector in the sequencefor the BTI (1404). The STA may determine the time at which the CP maytransmit to its selected sector (1406). For example, if the CP is usinglogic to reduced beacon length, e.g. the logic 900, the STA may assumethat beacons earlier in the sequence may not include associated-stationIEs. The STA may produce an estimate of the earliest time for the STA'sselected sector in the sequence. The STA may turn on its receiver atand/or after the time at which the CP may transmit. (1408). The STA mayreceive the beacon for its selected sector (1410).

As discussed above, a STA may, in some implementations, turn off itsreceiver and antenna after receiving a beacon with associated-stationIEs, and turn on its receiver and antenna at the end of the BTI.

In some cases, a STA using reception logic, e.g. 1300, 1400, may turn ONits receiver for a shorter duration than the duration of the BTI. Thismay result in power savings. In an example scenario where CP transmits16 beacons of 70 bytes in a beacon interval as part of the SLS, anassociated STA may have its receiver on for 528×16=8448 μs. A STA usingreception logic, e.g. 1300, 1400, may have its receiver on for 528 usfor the same scenario. The STA can save 8448 μs−528 μs=7.92 ms worth ofpower for the beacon intervals, which may occur at 100 ms intervals.

In various implementations, the CP and/or associated STA(s) may beportable devices. Portable devices may be moved, and the relativeposition of the associated STA(s) to the CP may change. In some cases,the PCP may update the selected sector information for associatedSTA(s). The CP may perform this update at regular intervals oraperiodically. For example, an update may be triggered. Triggers mayinclude signal quality reductions, indication of motion from sensors.Alternatively or additionally, the non-CP STA may request an update.Signal quality reductions may include changes in channel qualityindicators, decreases in SNR, and/or other signal quality reductions.Indications of motion from sensors may include output fromaccelerometers, gyroscopes, GPS sensors, and/or other motionindications. Triggers may occur on a non-CP STA and the non-CP STA mayinitiate an update request. The updates to the selected sector may alsomitigate the effects of an object that may be block or partiallyblocking a transmission path. In some cases, such as a blocking object,updates to the selected sector may provide transmission/receptionimprovements in the absence of motion and/or relative motion among theCP and associated STAs, e.g. for stationary or non-portable STAs.

FIG. 15 shows example logic 1500 for receive sector updates. The STA maydetect a trigger event (1502). In some cases, a STA may respond to aTXSS from a CP or other initiator with a RXSS. A lost beacon or a signalquality reduction may trigger a RXSS by the STA. The STA may perform areceive sector sweep (RXSS) (1504). The STA may report its selectedreceive sector to the CP (1506). For example, the STA may configure itsantenna for directional reception via its AWV. The STA may then reportthe selected AWV or a corresponding sector ID to the CP. This may beseparate from the transmit AWV determined during TXSS. The CP may updatea database or listing of selected transmit and receive sectors for theSTAs. Additionally or alternatively, the STAs may store selectedtransmit and receive sectors. Updates to these selected sectors mayallow the CP and STSs to mitigate potential signal disruption frommovement or blocking objects in a dynamic environment.

The STA may report its selected sector via sector sweep (SSW) feedback.The STA may perform an RXSS. After the RXSS, the STA may send a SSWacknowledgement (ACK) to the CP indicating selected sector reception.

In some implementations the CP may transmit beacons to its antennasectors including sectors lacking associated STSs. The CP may transmitbeacons to sectors lacking associated STSs to enable unassociated STSsto become aware of CP and the associated network, and join the network.In some implementations, the CP may repeat sector sweeps at the beaconinterval.

Associated STSs receive beacons at the beacon interval to remainsynchronized with the network. The STSs may use beacons to sync theirsTSFs with that of the CP. Additionally or alternatively, the STSs mayuse beacons to determine the channel access schedules. If a STA missesmultiple beacons over a period the STA may lose synchronization with theCP and/or be unable to schedule data transmission.

Unassociated STSs may not be synced with the CP. Unassociated STSs maynot use regular beacon transmission from the CP prior to joining thenetwork. If the CP does not send a beacon to a receive sector forunassociated STA in a beacon interval or for a number of beaconintervals, the unassociated STA may experience delays in connecting tothe network. For example, in scenario with a beacon interval of 100 ms,if an unassociated STA misses 10 beacons in a row, the STA may take 1 slonger to join the network. In some cases, increasing time to join thenetwork may not affect performance. For example, some latency in joiningmay be expected. Lost connections for associated devices may have alower tolerance.

In some implementations, the CP may selectively transmit beacons toselected transmit sectors for associated STA(s) and transmit beaconsless frequently to the rest of the sectors. This may reduce the averageduration of the BTI.

FIG. 16 shows an example timing diagram 1600 for beacon intervals. Inbeacon interval 0 1602, beacons are transmitted to all N sectors 0 toN-1 1614. For beacon intervals 1 to n-1 1604, 1606, beacons aretransmitted only to sectors 2 and N-1 1606, which are selected sectorsfor associated STAs in this example scenario.

FIG. 17 shows example logic 1700 for beacon transmission. The CP mayselect a sector for transmission by generating a pseudo-random sector IDfrom via its sequence generator (1702). The CP may compare the generatedsector ID to a listing of selected sectors for associated STA (1704). Ifthe comparison indicates that the generated sector ID corresponds to aselected sector, the CP may transmit a beacon (1706). Otherwise, the CPmay determine if a beacon may be transmitted to an unassociated sector,e.g. a sector where there are no associated STAs (1708). If the CP maytransmit to an unassociated sector, the CP may transmit a beacon (1706).If the CP may not transmit to an unassociated sector, the CP may forgotransmission of a beacon to the sector (1710). The process may berepeated for the antenna sectors of the CP (1712).

The determination of whether a beacon may be transmitted may be based ona transmission scheme. For example, in a given transmission scheme, theCP may transmit beacons to unassociated sectors at intervals of multipleBTIs, e.g. skip 1, 2, 3, 10 or other number of BTIs. In someimplementations, for a transmission scheme, the CP may staggertransmission of beacons to unassociated sectors, e.g. transmit to arotating fraction of the unassociated sectors in intervals of theinverse of the fraction of BTIs. For example, transmit to a rotating 20%of the unassociated sectors intervals of 5 BTIs. In such cases, thelength of the BTI may remain stable. In some cases, where the number ofunassociated sectors may not be divided evenly, a rotating unassociatedsector may receive a beacon to maintain the stable length of the BTI.For example, an interval of 5 BTIs, e.g. 4 skipped for one sent, isused, every 100 BTIs a given unassociated sector may receive a beaconafter 3 skipped BTIs. This may be analogous to a leap year system.

Additionally or alternatively, associated-station IEs may not betransmitted for the unassociated sectors using the logic 1700.Associated-station IEs may be transmitted to associated sectors.Reducing the number of transmitted beacons and/or their payload size mayreduce power consumption and bandwidth committed to the BTI.

FIG. 18 shows an example beacon transmission environment 1800. In theexample environment 1800, a CP is transmitting beacons over 6 sectors1801, 1802, 1803, 1804, 1805, 1806 (sector IDs 0 to 5). The CP 1822 hasone associated STA 1823. The STA 1823 is receiving beacons with itsantenna configured in a quasi-omnidirectional receive pattern 1824. TheCP 1822 repeats transmission of beacons with the BTI for the associatedSTA 1823 in sector ID 2 1803. The remaining sectors 1801, 1802, 1804,1805, 1806 receive beacons less frequently. Additionally oralternatively, associated-station IEs may be transmitted in sector ID 21803, and the associated-station IEs may be withheld for transmissionsto the remaining sectors 1801, 1802, 1804, 1805, 1806.

The methods, devices, and logic described above may be implemented inmany different ways in many different combinations of hardware, softwareor both hardware and software. For example, all or parts of the systemmay include circuitry in a controller, a microprocessor, or anapplication specific integrated circuit (ASIC), or may be implementedwith discrete logic or components, or a combination of other types ofanalog or digital circuitry, combined on a single integrated circuit ordistributed among multiple integrated circuits. All or part of the logicdescribed above may be implemented as instructions for execution by aprocessor, controller, or other processing device and may be stored in atangible or non-transitory machine-readable or computer-readable mediumsuch as flash memory, random access memory (RAM) or read only memory(ROM), erasable programmable read only memory (EPROM) or othermachine-readable medium such as a compact disc read only memory (CDROM),or magnetic or optical disk. Thus, a product, such as a computer programproduct, may include a storage medium and computer readable instructionsstored on the medium, which when executed in an endpoint, computersystem, or other device, cause the device to perform operationsaccording to any of the description above.

The processing capability of the system may be distributed amongmultiple system components, such as among multiple processors andmemories, optionally including multiple distributed processing systems.Parameters, databases, and other data structures may be separatelystored and managed, may be incorporated into a single memory ordatabase, may be logically and physically organized in many differentways, and may implemented in many ways, including data structures suchas linked lists, hash tables, or implicit storage mechanisms. Programsmay be parts (e.g., subroutines) of a single program, separate programs,distributed across several memories and processors, or implemented inmany different ways, such as in a library, such as a shared library(e.g., a dynamic link library (DLL)). The DLL, for example, may storecode that performs any of the system processing described above.

Various implementations have been specifically described. However, manyother implementations are also possible.

What is claimed is:
 1. A method, comprising; determining a transmissionantenna weight vector for transmission of a first directional beacon toa first sector; transmitting, from a control point configured with theantenna weight vector, the first directional beacon to the first sector;receiving a selected sector indicator, at the control point, from astation in the first sector; in response to the selected sectorindicator, changing a selected sector listing in the control point; andresponsive to the selected sector listing, determining to transmit asecond directional beacon to the first sector.
 2. The method of claim 1,further comprising adding an associated-station information element tothe second directional beacon.
 3. The method of claim 1, where receivingthe selected sector indicator comprises receiving an associationresponse message from the station.
 4. The method of claim 1, where thedetermining to transmit the second directional beacon to the firstsector comprises determining to transmit the second beacon during abeacon transmission interval (BTI).
 5. The method of claim 4, furthercomprising determining to forgo transmission of a third directionalbeacon to an unassociated sector during the BTI.
 6. The method of claim5, where determining to forgo the transmission of the third directionalbeacon comprises determining that the unassociated sector isunassociated by comparing the unassociated sector to the selected sectorlisting.
 7. The method of claim 1, where transmitting the firstdirectional beacon comprises transmitting a sector identifier in thefirst directional beacon.
 8. The method of claim 1, further comprisingperforming a sector sweep responsive to the first directional beacon,the sector sweep comprising transmitting sweep beacons to antennasectors.
 9. The method of claim 8, where the receiving the selectedsector indicator occurs responsive to the sector sweep.
 10. The methodof claim 9, further comprising: adding an associated-station informationelement to the first directional beacon; and omitting theassociated-station information element from the second directionalbeacon.
 11. A system, comprising; a control point comprising: adirectional antenna characterized by a vector; and control logiccomprising a data path to the directional antenna, the control logicconfigured to: send, to the vector, a vector value for a transmissionsector; transmit a first beacon to the transmission sector; andresponsive to an association, transmit a second beacon; and a stationdisposed in the transmission sector, the station comprising; a stationantenna; and station logic, in communication with the station antenna,the station logic configured to: receive the first beacon from thecontrol point; responsive to the first beacon, perform the associationwith the control point; and receive the second beacon.
 12. The system ofclaim 11, where the second beacon comprises an associated-stationinformation element.
 13. The system of claim 12, where the first beaconlacks the associated-station information element.
 14. The system ofclaim 12, where the control logic is further configured to transmit thesecond beacon during a beacon transmission interval (BTI).
 15. Thesystem of claim 14, where the control logic is further configured toomit transmission of a third beacon to an unassociated sector during theBTI.
 16. The system of claim 14, where the station further comprises astorage device, in data communication with the station logic, thestorage device comprising a transmit antenna sector identificationpattern (TAID) information element, the TAID information elementconfigured to identify a beacon transmission sequence for the BTI. 17.The system of claim 16, where the station logic is further configuredto: based on the beacon transmission sequence for the BTI, predict aduration of the second beacon within the BTI; and power off the stationantenna outside of the duration.
 18. A device, comprising; a directionalantenna comprising a phased array, the phased array characterized by anantenna weight vector; a data storage apparatus comprising: anassociated-station information element; and a selected sector listing;and transmission logic comprising: a data path to the data storageapparatus; a transceiver path to the directional antenna; and thetransmission logic configured to: identify a sector for transmission ofa beacon; determine the antenna weight vector value for the sector;send, via the transceiver path, the antenna weight vector value to thephased array; compare, using the data path, the sector with the selectedsector listing; responsive to the comparison, add the associated-stationinformation element to the beacon; and transmit, via the directionalantenna, the beacon with the associated-station information element. 19.The device of claim 18, where the associated-station information elementcomprises a schedule for a data transmission interval access period. 20.The device of claim 18, where the transmission logic is furtherconfigured to identify a second sector for which the transmission logicforgoes subsequent transmission of a different beacon.